Light from electron levels, but radio from AC?

[mrneglect]

I know that light (such as that emitted by a fluorescent bulb) is generated by electrons falling into lower energy states and releasing an amount of energy as a photon. But radio is transmitted by producing an alternating current in a conductor, and (I assume) it's the acceleration and deceleration of this electric charge which creates the changing electromagnetic field which propagates away from the source.

Can light be produced in the same way? Is it feasible to produce an alternating current in the order of 600THz? If so, could we produce things like sawtooth, triangle and square light rather than the usual sinusoidal?

I have a feeling there's some 'springyness' to electron interaction and it would be difficult to produce a frequency of 600THz in any conductor larger than about 500nm, but I'd like to hear some thoughts on it.

Similarly, do any atoms contain such close-together energy levels that an electron might produce something in the order of kHz or MHz when it falls to a lower energy level, or do all radio waves have to come from some kind of alternating current?

 

[Bob S]

The atomic hydrogen line known as the 21 cm line or the 1420 MHz line is observed in intersteller hydrogen gas. It is hyperfine structure of electrons in the 1s state, and can be both emitted and absorbed by the hydrogen gas. The 1420 MHz line is one of the most popular lines used in the SETI (Search for Extraterrestrial Intelligence) search. This frequency can be generated by both atomic transitions (masers) and by microwave oscillators. It is roughly 60% the frequency in microwave ovens. See
http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html

 

[mrneglect]

Aha, OK, so you can get some pretty low energy photons coming out of atoms, but what about high energy photons out of alternating current? Is there some maximum cut-off there too?